阴离子交换树脂回收土壤淋洗液中的EDTA-Cd

Recovery of EDTA-Cd complexes in soil leacheate using anion exchange resins

以湖南株洲污染土壤作为研究对象,研究了Na-EDTA、NH_4-EDTA、Ca-EDTA在不同浓度下对土壤中Cd的去除效果,确定出适合的浓度与淋洗剂;并采用氯型717阴离子交换树脂对土壤淋洗液中的EDTA-Cd络合物进行吸附与回收试验,主要方法流程如下:采用静态法考察了固液比、pH值、时间、温度对树脂吸附EDTA-Cd络合物的影响,确定最佳吸附条件;采用上柱吸附法研究了在不同流速下穿透曲线的变化,确定树脂的穿透点;选取Fe_2(SO_4)_3多价金属盐溶液作为再生剂,对树脂中的EDTA-Cd络合物进行动态洗脱回收,测定出洗脱曲线与体积.随后进行连续5次吸附洗脱试验,探究树脂的再生性与树脂中EDTA-Cd络合物的回收效果.结果表明,在浓度为2.5 mmol·L^(-1)时,Na-EDTA、NH_4-EDTA、Ca-EDTA溶液对土壤中的Cd具有较好的去除效果,其去除率分别为64.75%、66.11%、68.29%.另外,在静态吸附过程中,随着固液比增加,树脂对EDTACd的吸附效率减少,在pH值为5.6时,对EDTA-Cd络合物吸附效率达到93.53%,树脂达到吸附平衡所需的时间为30—45 min,最佳反应温度区间为25—35℃;在动态吸附回收过程中,当上柱流速为4 m L·min^(-1)时,树脂达穿透点所需EDTA-Cd络合溶液为650 m L;再生剂Fe_2(SO_4)_3的洗脱体积为60 m L,洗脱溶液与吸附EDTA-Cd络合物溶液的体积比例达到1∶10.经过连续5次吸附洗脱试验后,树脂对EDTA-Cd络合物的去除率和再生率分别达到76.64%—93.43%、75.65%—84.19%.利用氯型717阴离子交换树脂提取以及回收土壤淋洗液中EDTA-Cd络合物是可行的.

Contaminated soils by heavy metals were collected from Zhuzhou,Hunan Province. And the removal Cd in soil by Na-EDTA,NH4-EDTA,and Ca-EDTA at a variety of concentrations was investigated to select suitable concentration and washing agent. A chloride-type 717 anion exchange resin was then adopted for the adsorption and recovery of the EDTA-Cd complex in the soil leacheate.The main procedure as follows based on static method,the influencing factors such as solid-liquid ratio,p H,equilibrium time,temperature on anion resin for adsorption of EDTA-Cd complex were evaluated and the optimal conditions were established. A column adsorption study was carried out by setting a function of feed flow rate for the variety of the breakthrough curves,and breakthrough pointsof the resin were obtained. A dynamic elution experiment for recovering EDTA-Cd complex was performed on 717 anion exchange resin by using a Fe2（ SO4）3 solution as regenerating to analyze elution curves and volume. Five consecutive adsorption-elution cycles were applied to the resin in order to investigate the reusability of the ion-exchange resin and recovery rate of EDTA-Cd complex.The result showed that Na-EDTA,NH4-EDTA,and Ca-EDTA effect of Cd in soil at 2.5 mmol·L（-1）,and the removal rate was 64.75%,66.11%,68.29%,respectively. In addition,on the basis of the static process,the adsorption efficiency of EDTA-Cd complex decreased with the solid-liquid ratio increases. The removal rate of EDTA-Cd complex was 93. 53% at pH = 5.6,and the equilibrium adsorption was reached within 45 min. The optimum temperature range was 25—35 ℃. A column sorption-elution experiment showed that the resin reached the breakthrough volume of 650 m L at 4 m L·min（-1）; and the elution volume of Fe2（SO4）3 was 60 m L,which was 1 ∶10 to the volume of EDTA-Cd complex. The adsorption efficiency of the resin and recovery rate of EDTA-Cd complex still reached 76. 64%—93. 43% and 75. 65%—84. 19%,respectively after five cycles. This method is feasible and suitable for the extraction and recovery of EDTA-Cd complex in soil leacheate.